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Homeowner's Guide for Flood, Debris and Erosion

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Homeowner's Guide for Flood, Debris and Erosion Homeowner’s Guide for Flood, Debris, and Erosion Control after Fires The assistance of the following agencies and publications in preparing this guide is gratefully acknowledged: Homeowner’s Guide for Flood, Debris, and Erosion Control published by the Los Angeles County Department of Public Works Homeowners Guide for Flood Prevention and Response published by Santa Barbara County Flood Control and Water Conservation District Stormwater Best Management Practice Handbook for Construction Activities California Stormwater Quality Association (CASQA), January 2003 Table of Contents After the Fire .................................................................... 1 Getting Prepared ............................................................. 3 Methods for Protecting Your Property .......................... 6 Flood Insurance ............................................................. 11 Glossary of Terms ......................................................... 12 *This information is provided to assist residents with erosion control, but not all circumstances are alike. Home owners should consult an erosion control professional for assistance with more difficult circumstances. After the Fire The effects of fire can be felt long after the flames are extinguished. Rates of erosion and runoff can increase to unsafe levels when trees, shrubs, grasses and other groundcover are no longer present. Under normal circumstances, roots help to stabilize soil, while stems and leaves slow water down, giving it time to absorb or soak into the soil. These protective functions can be severely compromised or even eliminated by fires. In the aftermath of a fire, the potential for flooding, debris flows, and erosion is greatly increased. Fortunately there are many things you can do to protect your home or business from the damaging effects of a fire: Flooding - Flooding may occur even during moderate storms as rain falls on areas where vegetation has been destroyed by fire. Remember that flood waters: o Consist of large quantities of water, and are often very turbulent and murky due to fine sediment, ash, and soil. o Flood waters can quickly reach depths that would pose a threat to people or automobiles. o Inundate large areas and can damage or destroy structures in their path. Debris Flows - Debris flows are equally dangerous, especially in hillside or mountainous areas. Remember that debris flows: o Consist of large quantities of soil, rocks, boulders, trees, or brush moved by flood waters. o Occur when flood waters flow over barren soils and burn areas. o Are highly destructive and may leave large quantities of sediment and rocks in their paths. o Contain sufficient strength to destroy objects in their path. o Can be controlled or directed to reduce property damage. Erosion - Erosion often results in areas where there are steep banks of scoured soil or other ground materials. Remember that erosion: o Cannot be controlled while it is happening and is often not seen until flood waters have subsided. o Can seriously undermine structures, often leading to major structural failures. o Occurs most often when waters flow rapidly over loosely compacted soil or burn areas. o Can be reduced by stabilizing slopes prior to storms. Figure 1 provides a general illustration of the types of actions you can take to protect your property from those hazards mentioned above. The remainder of this guide provides more detailed descriptions of these and other recommended practices that you can take to protect your home and property. 1 Revised August 2015 An Unprotected Home A Protected Home Figure 1: Examples of Unprotected vs. Protected Homes Revised August 2015 Getting Prepared Evaluating your Property After a fire, it is important to thoroughly evaluate and plan for storm events in order to help protect your property. First, start by determining where water and debris are likely to flow and collect. Once you have located potential routes where water and debris may flow, plan and implement diversions in those identified flow pathways. Pay particular attention to steep, barren slopes, low spots, and high flow areas when planning for structure and property protection. General Precautions During a storm event, property damage can be attributed to stormwater runoff, debris (mud, rocks, branches, etc.), or both. When devising a protection strategy for your property, pay special attention to the following general rules: o Never underestimate the power of stormwater and debris flows. o Try to direct stormwater and debris flows away from any structures. o Avoid altering natural or existing drainage patterns in a way that might worsen conditions for you or your neighbor. Work cooperatively with your neighbor to achieve the best results. o Avoid trying to control or confine flows more than is absolutely necessary; remember that the water and debris flows need to go somewhere. o Place protection devices in such a way so as to deflect debris; do not try to create a dam or stop the flows in any way; this may cause flooding. o In extreme condition, board up windows as necessary to prevent debris from entering structures. o Protect your most valuable property first - your home; then consider what time and money are available to protect other less valuable objects such as swimming pools, landscaping, or other minor structures. o Be prepared to sacrifice the use of portions of your property to achieve the greatest amount of protection. o Don’t take unnecessary risks; if your debris control problems appear to warrant solutions beyond the scope of this guide, consult a competent expert such as a civil or geotechnical engineer or a landscape architect for additional advice. Materials and Supplies There are many effective and relatively inexpensive do-it-yourself ways to control flows. Most can be installed with normal household tools using materials available at your local lumber yard or hardware store. Materials that you may need to implement the specific methods 3 Revised August 2015 described in this guide typically include sandbags, gravel bags, fiber rolls, lumber, plywood, plastic sheeting, rubber seals (similar to weather stripping), and concrete blocks. Maintenance of all erosion control devices along with the routine removal of accumulated water and debris is crucial to avoid potential flooding problems and structural damage. When not routinely maintained, erosion control devices may become ineffective. In addition, all drainage pathways should be kept clear of debris and overgrowth since blockage may cause flooding and structural failure. Typically, maintenance of hillside drains is the responsibility of the property owner. Sandbags - Sandbags are commonly used for a variety of specific purposes to prevent property damage. Properly filled, installed, and maintained sandbags can be used very effectively to re-direct stormwater and debris flows away from property improvements. Figure 2 below provides general instructions for filling and placing sandbags. Note: sand bags should NOT be used on a slope or hillside. o Fill sandbags one-half full. Sand is suggested if readily available; however, any local soil may be used. o For a more durable bag with increased effective life, mix 10 parts of sand or soil with one part of cement. The materials can be mixed and placed dry. After all bags are in place, a light sprinkling of water is recommended. o If you do not have tie closures for the bags, fold the top of the sandbag down and place the bag on top of the folded top. It is important to place bags with the folded top in an upstream or uphill direction to prevent bags from opening when water runs by or over them. Figure 2: Instructions for Filling and Using Sandbags To ensure their effectiveness, care should be taken to properly stack sandbags. Figure 3 illustrates a number of ways in which sandbags can be used, each showing their proper placement. When stacking sandbags, make sure that each layer is completed prior to starting the next one. Also limit placement to two layers unless a building is used as a backing or the sandbags are stacked in a pyramid fashion. It’s important to remember that there are limitations to using sandbags. They will not completely seal out water. Sand and soil filled sandbags also deteriorate when they’re exposed to the sun for extended periods of time, and from the continued wetting and drying over several months; if the bags are placed too early, they may not be as effective when it rains. Finally, sandbags are generally intended for low-flow protection (up to two feet). Protection from higher flows often requires a more permanent type of structure. Gravel bags are similar to sandbags except they are made of burlap and filled with small rocks (gravel). Gravel bags should be placed on slopes to minimize erosion. The burlap and gravel 4 Revised August 2015 allow stormwater to pass through the bag while trapping sediment upstream. Gravel bags should be placed across the slope not more than two high as shown in Figure 2. Remember to clean out the silt trapped behind the bags after each storm. Figure 3: Uses and Proper Placement of Sandbags 5 Revised August 2015 Methods for Protecting Your Property Each property is unique. Protective measures should always be selected to address your property and its surroundings. The following issues should be considered in developing a strategy: o Protecting structures o Protecting land from water and debris flows o Protecting slopes and surfaces from erosion Protecting Structures Several types of deflection devices can be used to protect structures, doorways, and windows on your property. For Doors and Windows - One way to protect doors and windows is to completely cover them with plywood. Low-grade plywood can be placed over windows, vents, and doors and should overlap 3 to 4 inches on all sides. Each sheet of plywood should be secured with four or more nails, screws, or bolts; stakes and boards may also be used to wedge barriers in place. When the plywood is no longer needed, it can be dismantled and stored for years to come.
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